The present invention relates to a display controller, a display system, and a display control method.
In recent years, a display device using an electroluminescent (EL) element has attracted attention. In particular, since an organic EL panel including an EL element formed using a thin film of an organic material is a self-emission type, a backlight becomes unnecessary, whereby a wide viewing angle is implemented. Moreover, since the organic EL panel has a high response speed in comparison with a liquid crystal panel, a color video display can be easily implemented by simple configuration.
The organic EL panel is divided into a simple matrix type and an active matrix type in the same manner as the liquid crystal panel. When driving a simple matrix type organic EL panel, grayscale control may be performed using pulse width modulation (hereinafter abbreviated as “PWM”). A display controller performs grayscale control by outputting control signals to drivers (data driver and scan driver) which drive the organic EL panel.
The data lines of the organic EL panel may be driven using a plurality of data drivers. The data drivers are cascade-connected. Display data and various synchronization signals are supplied to the cascade-connected data drivers from the display controller. The data driver latches the display data in synchronization with the synchronization signal from the display controller, and supplies drive signals corresponding to the latched display data to the data lines.
However, if the data drivers perform a switch operation of several hundreds of bits of display data at the same time, a peak current is increased due to an increase in shoot-through current or the like. This may cause the power supply voltage of the data drivers to be decreased.
In a liquid crystal display panel, since a liquid crystal element which makes up the liquid crystal display panel has a low response speed, the effect caused by a decrease in power supply voltage rarely influences the display quality of the panel. However, since the organic EL element has a high response speed, the display quality of the organic EL panel may be affected by a decrease in power supply voltage of the data drivers.
In order to prevent such a decrease in power supply voltage, it is effective to make the peak current generation timings of the data drivers different from each other. The generation timings may be made different from each other by delaying the synchronization signal from the display controller by using a buffer circuit or the like. However, the adjustment target timing differs depending on the type of organic EL panel, compatibility between the data driver and the organic EL panel, manufacturing variation, and the like. In particular, since the organic EL element has a high response speed, the display quality deteriorates even if the adjustment target timing differs to only a small extent. This makes it necessary to adjust the timing for each product, thereby causing problems such as an increase in the number of parts accompanying adjustment, an increase in design cost, and an increase in the number of development steps.
In the case of driving the scan lines of the organic EL panel using a plurality of scan drivers, the display quality of the organic EL panel may be affected when the scan drivers perform the switch operation at the same time. The above-described problem occurs not only in the case of driving the organic EL panel, but also in the case of driving a display panel including other display elements having a high response speed.